State of the Art
Although decalins and other bi- and polycyclic naphthenes have been recognized as excellent potential components of high-energy turbine jet fuels for three decades, there is presently no commercial process to produce specifically these type of hydrocarbons as a part of the multi-billion dollar jet fuel market. The technologies for hydrogenation of naphthalenes and other aromatics have been available for more than two decades, but commercializing such processes is hampered by the high cost of hydrogen.
Some work on alternative processes for producing decalins by dehydrodimerization (self-condensation) of monocyclic naphthenes can be found in the literature. Unfortunately, there are severe limitations in the usefulness of this previous work for the following reasons: (1) the studies were carried out over 40 to 50 years ago when product analysis was limited and difficult; (2) the experiments were performed mainly for the purpose of understanding the reaction mechanisms of commercial alkylation processes of isobutane with butenes, and, therefore, light olefins (C.sub.2 -C.sub.4) were used as alkylating agents. Consequently, the main products consisted of alkylated monocyclic naphthenes accompanied by minor quantities of decalins as by-products. The alkylcyclohexanes obtained were in the C.sub.8 -C.sub.11 range and were not suitable for use as advanced jet fuels; (3) there was insufficient information about how operating variables affect the product distribution.
It has been pointed out previously that alkylsubstituted decalins and other polycyclic naphthenes can be utilized as high quality jet engine fuels. The possibility of producing such hydrocarbons, however, has not attracted in the past the interest of the petroleum refining industry in spite of the fact that some of the potential precursors, e.g., alkylcyclopentanes, are found as abundant oil components.
In summary, there has been a need to extend the limited previous studies toward a well-defined purpose, i.e., the development of new processes for advanced jet fuels. While previous indications existed of self-condensation of methylcyclopentane in the presence of olefins, very little had been explored with respect to monocyclic naphthenes and higher, i.e., C.sub.5 -C.sub.8, olefins which were selected as reactants for the study of acid-catalyzed self-condensation and alkylation reactions directed towards obtaining jet fuel range naphthenic hydrocarbons. Complete analysis of the products, using modern analytical methods, e.g., gas chromatography-mass spectrometry, Fourier transform infrared spectrometry (FTIR), and uC NMR, was performed, allowing for an elevation of the feasibility and the commercial potential of the self-condensation and alkylation reactions studied.